1. Field of the Invention
The present invention relates to a battery system optimized for a car power source apparatus that supplies electric power to a motor that drives the vehicle, and in particular to a battery system that detects excessive current and cuts-off current flow with a fuse and relays.
2. Description of the Related Art
A battery system has been developed with a series connected fuse and relays to prevent excessive battery current. (Refer to Japanese Patent Application Disclosure 2008-193776.) As shown in FIG. 1, the battery system of Japanese Patent Application 2008-193776 has a battery 91 divided into two battery blocks 95, and those battery blocks 95 are connected in series via a fuse 98. In addition, the battery system has relays 92 connected to the output-side of the battery 91. In this battery system, if excessive current flows in the driving battery, the fuse 98 blows and cuts-off battery 91 current. Furthermore, a control circuit 94, which controls the relays 92 ON and OFF, switches the relays 92 OFF to cut-off battery 91 current. The battery system control circuit 94 is provided with a current detection circuit 99 to detect battery 91 current, and battery 91 charging and discharging is controlled based on the detected current. The current detection circuit 99 detects current within the normal battery 91 charging and discharging range, for example, at or below 200 A for a car battery system. If a current greater than this flows in the battery, namely if abnormal high current flows in the battery, the relays are switched OFF to cut-off battery current. The battery system of FIG. 1 achieves a high degree of safety by blowing the fuse 98 or switching the relays 92 OFF in an excessive current condition.
However, it is possible for the battery system shown in FIG. 1 to be unable to blow the fuse 98 and switch the relays 92 OFF in an excessive battery 91 current situation. This is because when excessive current is detected and the relays are controlled OFF, it is possible for relay contacts to fuse together due to the high current and prevent the relays from being switched OFF. If an attempt is made to cut-off current exceeding the maximum cut-off current of the relays, relay contacts can fuse together by arcing during the cut-off attempt. Therefore, the battery system shown in FIG. 1 has the drawback that when the control circuit 94 detects excessive battery 91 current and controls the relays 92 OFF, relay 92 contacts can fuse together preventing cut-off if the current is greater than the maximum cut-off current of the relays 92.
The first object of the present invention is to avoid the drawback described above. Thus, it is an important object of the present invention to provide a battery system that can reliably cut-off battery current without fusing relay contacts.
Further, internal current cut-off sections can be provided such as current interrupt devices (CIDs) that cut-off current when battery charging conditions become abnormal. These internal current cut-off sections cut-off current under abnormal battery charging conditions to ensure battery safety. For example, a CID internal current cut-off section insures battery safety by cutting-off current when internal battery pressure becomes abnormally high. Since the CID activates to cut-off current when the battery has been over-charged and internal pressure has increased to an abnormal level, a condition where the CID has cut-off current is a condition that retains the battery in its over-charged state. Consequently, while CIDs are safety assuring devices, it is important to limit their operation as much as possible. Incidentally, since a CID is designed to cut-off current, its ability to withstand high currents is low relative to other battery structural elements. Therefore, it is possible for a CID to cut-off current as a result of excessive current alone.
The second object of the present invention is to address this drawback. Specifically, the second object of the present invention is to provide a battery system that does not activate the battery CID, but rather can reliably cut-off excessive battery current with the fuse and relays.